Photochromic polymers, that is, polymers which contain photochromic groups in a macromolecule, are materials of significant technological potential in many industrial fields. For example, such polymers can be used in the manufacture of the plastic material of eye lenses and the manufacture of windows for the automobile industry.
Spirooxazines and their use in photochromic lenses have been recently reviewed by Crano et al., 1992. There has also been a significant amount of research reported on a number of side-chain photochromic polymers in which photochromic spiropyran or spirooxazine side groups are attached to a main chain through a flexible spacer (Krongauz, 1990, 1992). The structure of these compounds allows incorporation of a very high content of a photochrome in a polymer which can reach 100%. That is, each structural unit of the polymer contains the photochromic group. Properties of such polymers can be substantially different from the properties of the polymers containing photochromic molecules as solute, as photochromic compounds have been usually employed in photochromic lenses. Such solutions in polymers have inherent restrictions in solubility of the photochromic compound.
U.S. Pat. No. 5,322,945 (Krongauz et al.), assigned to the present applicants, describes spirooxazine photochromic polysiloxanes having an advantage over other spirooxazine photochromic compounds by giving high quality coatings for plastic lenses. However, these photochromic polysiloxane coatings exhibit rather low fatigue resistance against illumination with light.
European Patent EP 162524 describes organic polymer stabilizing compounds, which are derivatives of 2,2,6,6-tetramethylpiperidine, 2,2,6,6-tetramethylmorpholine or of 2,2,3,5,5-pentamethylpyrrolidine carrying a silyl group, which is capable of being hydrolyzed to silanol and is bonded to the ring structure by an Si--C bond. These compounds contain a sterically-hindered amino group together with a hydrolyzable silyl group, and are said to be able to stabilize organic polymers in general, and in particular homopolymers and copolymers of olefins and diolefins, such as polypropylene, polybutadiene and polyethylene of high and low density, especially towards ultraviolet radiation.
The reactive stabilizing compounds can give rise to resinification reactions, or can be anchored to a support or to the polymer to be stabilized, these characteristics enhancing the permanence of the stabilizer in the polymer.
The present inventors have tried to add the stabilizing compounds described in EP 162524 to photochromic polysiloxanes, particularly those described in U.S. Pat. No. 5,322,945. However, the maximum amount of such stabilizing compounds that could be added to the photochromic polysiloxanes without phase separation was less than 1% in relation to the polysiloxanes, such mixtures not giving any detectable protection against fatigue.
It would be highly desirable to provide new photochromic polysiloxane polymers that give high quality coatings for plastic lenses and give a significant protection against fatigue produced by light.